Background: Most eukaryotes are heterozygous, comprised of two distinct alleles. However, little is known about how distinct alleles are differentially expressed and regulated and whether differential regulation can confer fitness to an organism. The proposed studies will provide important information as to the extent of allele specific expression, its mechanisms and function. These topics are highly relevant to understanding mechanisms of cancer. Objective/hypothesis: The natural heterozygosity of C. albicans has allowed it to evolve and adapt to thrive in its mammalian host. However, the degree of differential allelic expression and the mechanism of its regulation are yet to be fully elucidated. I propose to determine the extent of differential allelic expression, and to elucidate if differential binding of specific transcription factors under fungal dimorphic conditions regulates this differential allelic expression. This work is expected to provide insights into the extent and role of heterozygosity of eukaryotes in general. Specific Aims: 1) Globally examine the extent of differential allelic expression in Candida albicans. 2) Determine if differential gene expression is associated with differences in binding of Poll I and transcription factors. 3) Assay the function of differentially regulated alleles. Study Design: I plan to study differential allelic expression and regulation using C. albicans as a model system. I will use 454 DNA sequencing methods to globally analyze allele specific gene expression. ChlPSeq. (chromatin immunoprecipitation and sequencing) will be used to assess how much is due to transcriptional regulation. Finally, I will determine the function of differential allelic expression using gene replacement methods. Relevance: A hallmark of cancer is genome instability. This can be caused by hypomethylation and/or loss of heterozygosity. Moreover, it is common for specific chromosomes and specific chromosomal regions to be preferentially amplified. Thus, basic understanding of the diversity of allele specific expression and how it can be controlled is of high importance to cancer. Moreover, C. albicans is an opportunistic pathogen that affects many diseases, including cancer. Understanding mechanisms that control its growth and switch to dimorphic growth, which is involved in pathogenesis, is of significance for treatment of cancer patients.